Disorders of the heart valves usually involve both stenosis and regurgitation. In cases of valve disease incident to juvenile rheumatic fever, for example, valvular damage occurs when anti-streptococcal antibodies attack valve tissue as well as the causal bacteria, inflaming the valve cusps and forming lesions. The lesions then, in time, fuse and narrow the opening of the valve. As the movement of the cusps of the valve becomes impaired, the valve can no longer seal properly when closed and therefore some blood leaks backward with each heartbeat. This narrowing of the opening and restriction of blood flow is known as stenosis; the backflow of blood is called regurgitation. Stenosis and regurgitation together result in net loss of blood flow volume. Serious valve disease leads predictably to cardiac insufficiency, cardiac failure and--unless otherwise forestalled--the death of the patient. Surgical repair of damage incident to valve disease has been and will continue to be an important area for improvement and innovation in the battle against heart disease.